Manage domains and subdomains between multiples app engine/compute engine instances

By far the easiest way to do this is to create a wildcard DNS record for example.com. for example

*.example.com. 14400 A 10.10.10.10

or a CNAME

*.example.com CNAME example.com.

Remember that Apache will serve the content of the first vhost whose ServerName or Serveralias matched the Host: header in the http request. If none of these match then the content of the first vhost defined is served as it is considered the default vhost.

To get apache to server content the easiest way is to use NameBasedVirtual hosting.

If you want to server the same content from each vhost then just define one

NameVirtualHost *:80
<VirtualHost *:80>
    ServerName example.com
    DocumentRoot /var/www/html
    ...
</VirtualHost>

If you want to serve different (but the same) content from sub1.example.com and sub2.example.com then you could do something line this

NameVirtualHost *:80

<VirtualHost *:80>
    ServerName sub1.example.com
    ServerAlias sub2.example.com
    DocumentRoot /var/www/sub1sub2
    ...
</VirtualHost>

<VirtualHost *:80>
    ServerName example.com
    DocumentRoot /var/www/html
    ...
</VirtualHost>

and so on.

If you have many of vhosts to setup and configure you may want to have a look at Apache's Dynamically configured mass hosting documentation.

As this is an old question without an answer that is still getting views, I am posting Kamran's last comment as an answer which points to the solution in this thread.